1. Field of the Invention
The present invention generally relates to the field of implantable heart stimulation devices, such as pacemakers, implantable cardioverter-defibrillators (ICD), and similar cardiac stimulation devices. More specifically, the present invention relates to a device for monitoring the status of a cardiac lead implanted in a human heart, a cardiac stimulator comprising such a device, a system comprising such cardiac stimulator and implantable lead, and a method for monitoring the status of a cardiac lead.
2. Description of the Prior Art
Implantable heart stimulators that provide stimulation pulses to selected locations in the heart have been developed for the treatment of cardiac diseases and dysfunctions. Generally, the stimulation pulses are delivered via implantable leads comprising stimulation electrodes for intracardiac delivery of electrical pulses. Furthermore, sensors may be provided within the heart, such as intracardiac sensors for sensing electrical activities and events within the heart, blood pressure, acceleration, and/or other physiological parameters. Such parameters may be used for adapting the energy content of the stimulation pulses for ensuring cardiac capture while avoiding unnecessary energy consumption, adapting the cardiac rate and cardiac output to the varying need of the patient, i.e. rate adaptation, etc.
The implanted position for the respective intracardiac electrode or sensor is dependent on its purpose. For instance, an intracardiac electrode arranged at the distal end of a cardiac lead for delivering stimulation pulses is generally implanted to be in contact with myocardial tissue. Following implantation, an ingrowth of the distal end containing the electrode into the myocardial tissue preferably occurs. A dislocation of the cardiac lead from the myocardial tissue may lead to a severe increase in the energy content of the stimulation pulses in order to effectuate capture, which of course will have a negative effect of the battery life of the cardiac stimulator. On the other hand, a sensor for sensing the intracardiac blood pressure is preferably located in the blood stream and not intended for ingrowth into myocardial tissue.
Another issue related to intracardiac electrodes, in particular for sensing electrodes intended to be placed in the intracardiac blood stream, is that tissue overgrowths, such as protein layers and clots of blood adhering to the sensing surface, may impair the sensing ability of the electrode.
Thus, for many intracardiac electrodes and sensors, the position thereof within the heart is important and there is a need for monitoring or detecting position changes that would effect the function of the electrode, cardiac lead and/or stimulator. Furthermore, a need also exists for monitoring possible overgrowth of intracardiac electrodes and sensors placed in the blood stream of a human heart.